The invention is concerned with magnetically driven centrifugal pumps whose rotor forms a unit with an impeller which is located in a rotary magnetic field. Pumps with magnetically driven rotors which have an airgap along a spherical surface show significant advantages relative to other centrifugal pumps, because the most unreliable elements of conventional centrifugal pumps, namely shafts, bushings and rotary seals, are eliminated. The driven rotor, which forms a rotating unit with the impeller, is not only magnetically coupled with the driving system, but at the same time is axially supported by a spherical bearing that cannot seize. The stationary part of the spherical bearing is mounted on a column that is fixed to the separation wall that separates the wet compartment from the dry compartment of the pump. This separation wall must be made from non-magnetic material with very low electric conductivity, high tensile strength, and extremely high chemical resistance. It is current practice to weld or braze the column to the separation wall. The difficulty arises because the welding seam or brazing metal never will have exactly the same electro-chemical potential as the untreated separation wall material. Welding and brazing, therefore, will cause local electrolytic corrosion that might lead to penetration of the separation wall.